Superregenerative circuits



July 16, 1935. w, VAN ROBERTS 2,008,21

SUPERREGENERATIVE CIRCUITS Filed Fb. 5, 1952 2 SheetS-Sheet'l INVENTOR WALTER VAN B. ROBERTS ATTORN EY y 1 1935- I w. VAN B, ROBERTS 1 2,008;261

SUPERREGENERATIVE CIRCUITS Filed Feb. 5, 1932 2 Sheets-Sheet 2 Y INVENTOR WALTER VAN B. ROBERTS ATTORNEY Patented July 16, 1935 SUPERREGENERATIVE CIRCUITS Walter van B; Roberts, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 5, 1932, Serial No. 591,073

14 Claims.

My present invention relates to regenerative systems, and more particularly to novel methods of, and means for, producing super-regeneration in receiving circuits.

In my copending application Serial No. 351,411, filed March 39, 1929, there has been disclosed a method of producing super-regeneration in a receiving circuit which comprises utilizing a reverse ieed-back action for rapid quenching of radio frequency oscillations during the damping period, without introducing appreciable damping into the oscillation circuit during the regeneratively amplifying, or building-up period. It was pointed out in the said application that the method of periodically reversing the phase of feed-back in a super-regenerative circuit was desirable because it insured building-down oscillations during the reversed feed-back period to .a slightly greater extent, due to the inherent resistance helping to build down, than they are built up during the direct feed-back period, thus preventing any spilling over into sustained radio frequency oscillation.

Specifically, my prior application disclosed a receiving circuit of the super-regenerative type in which a pair of tubes of similar characteristics was utilized, one of the tubes functioning as the amplifier and having a feed-back coil associated.

therewith, the other tube having a second feedback coil associated therewith and'iunctioning as a reverse feed-back means, the entire operation of the amplifying action being initiated by an interrupting super-audible frequency in such a manner that the reverse feed-back means commenced to quench oscillations in the amplifier tube prior to the instant when oscillations of the amplifier would otherwise attain an undesirable amplitude. Various advantages for this specific typeof superregenerative system were described in the aforementioned application. However, it will be observed that the means for providing the reversed feed-back action utilized an additionaltube.

Now, I have discovered a method of, and devised means for, utilizing the principle of the aforementioned application in connection with a single tube. That is to say, in the present application there is disclosed a method of, and means for, periodically reversing the phase of feed-back in a super-regenerative system, of a single tube. Essentially, rrangements disclosed in this application utilize an element of an electrically balanced bridge for alternately providing regenerative and degenerative feed-back between the output and input circuit of an amplifier tube, the periodic reversal of the phase of the feed-back being caused by the action of a source of interrupting frequency current in unbalancing the bridge. Accordingly, it may be stated that it is one of the prime objects of my present invention to provide a method oi, and means for, producing superregeneration in an electrical circuit including an electron discharge tube which comprises utilizing a reverse iced-back action for rapid quenching of the radio frequency oscillations during the damping period, the phase of the f ed-back being periodically reversed by unbalancing, at a predetermined rate, a normally balanced electrical system.

Another important object of the present invention is to provide a regenerative electrical circuit comprising a single tube provided with an input and output circuit, a normally balanced electrical system being disposed in one of said circuits, and means utilized in conjunction with the normally balanced system for varying one or more elements of the said system to periodically unbalance the system first in one direction and then in an opposite direction whereby the phase of feed-back between the output and input circuits of the tube will be periodically reversed and the circuit will operate in a super-regenerative manner.

Another object of the present invention is to provide a super-regenerative circuit consisting of a space discharge device provided with a tunable input circuit and an output circuit, a normally balanced electrical bridge being disposed in the output circuit, one of the elements of the bridge being coupled to the tuned input cirouit to transfer energy from the output circuit thereto, there being additional means provided for varying one or more elements of the bridge in such a manner as to periodically unbalance the bridge in opposite directions whereby the phase of ieed-back between the output and input circuits will be periodically reversed.

Still other objects of the present invention are to simplify the circuit shown in my aforementioned copending application wherein an additional tube is employed for securing the reversed phase feedback, and to more particularly provide a super-regenerative circuit which is not only reliable and eiiicient in operation, but economically manufactured and assembled.

The novel features which I believe to be characteristic of my invention are set forth inparticularity in the appended claims, the invention itselfphowever, as to both its organization and method of operation will best be understood by "eference to the following description taken in connection with the drawings in which I have indicated diagrammatically several circuit arrangements whereby my invention may be carried into effect.

In the drawings,

Fig. l' diagrammatically shows a circuit embodying the basic principle of the present inven tion,

Figs. 2 to '7 inclusive show. different specific embodiments of the arrangements utilizing the basic an electron discharge tube of any well known type. This tube may compriseior example, a

triode, it being clearly understood that any other type of tube well known to those skilled-in the art may readily be employed in the present invention. A parallel resonant circuit comprising an inductance coil L and a variable tuning condenser C is connected between the control electrode and the cathode of the tube 2 in the well known and usual manner. A source of biasing voltage C1 is connected in the control electrode circuit of the tube 2 to provide proper negative biasing voltage for the said control electrode or grid. Between the anode and cathode of the tube 2 there is connected a path including a normally balanced electrical system i, a reproducer 3,anda source of anode potential B. The reproducer 3 is specifically shown as being of the head set type, it being understood however that any other type of reproducer may be employed.

The balanced electrical system A specifically e comprises a bridge arrangement including arms 21, 22, a and 24. Each of these arms is in electrical nature an impedance, and is conventionally represented to denote that each impedance maybe of any desired specific electricalnature. Thus, these impedances may be resistive, or reactive, or complex, but preferably they should be so chosen that the equation of balance 21/zz=z3/e4 maybe satisfied for all frequencies. A coil T is connected, as the diagonal arm of the bridge between the pointsa and b, the'coil T being inductively coupled to the coil L.

It is to beunderstood that the resonant circuit L, C is not necessarily the signal collecting circult of the system shown in Fig. 1. It is possible to connect a pro-selector circuit, as for example, a tunable band pass circuit or a tuned stage of radio frequency amplification, or an untuned stage of radio amplification, or all three, or any two of these, between a signal collecting device,

as an antenna, and the resonant radio frequency circuit L, C. Additionally, it is quite obviousthat the circuit L, C need not necessarily be tunable to different frequencies, but may readily comis substantially equal to it will be obvious that no current can flow through the diagonal path including the coil T, sincejthe drop ofpotential between points a and I) must no essarily be equal to zero. In this balanced condition of the bridge circuit,ipoints a and b are at substantially the same electrical potential and'may be termed a pair of conjugate neutral points of the bridge or balanced electrical system. Hence, when the bridge 4 is balanced, the transfer of energy between thecoils T and L is at a minimum, and may be made even equal to zero. However, if one or more of the impedances e is varied from that value at which balance of the bridge is secured, obviously the bridge will be unbalanced and current will flow in one direction or the other through coil T.

Again, the direction of unbalance can be regu lated by varying a predetermined one or the impedances 2. By varying one or more of the im pedances a about the value giving a balance so as to periodically unbalance the bridge first in one direction and then' the other, the phase of the feed-back between coils T and L will be periodically reversed, and the circuit operated in a super-regenerative manner. In other words,the

ridge 4 is utilized, in conjunction with a device for periodically upsetting the bridge balance in alternately different directions, to provide a reverse feed-back between coils T and L for rapid quenching of radio frequency oscillations during a the aforementioned basicprinciple; Thus, in Fig.

2 the bridge 4 comprises a pair of iron core radio frequency chokes X1 and X2. The common terminal 5 or" the chokesis connected to one side of the reproducer 3, while the other terminals of the chokes are connected to opposite sides of the feed-back coil T which is coupled to coil L. The coil T has its mid-point 8 connected to the anode of tube 2. A source: of interrupting fre quency current F1 is "inductively coupled to both chokes Xi and X2, a radio frequency choke 7 being disposed in series with the source Fl in iii order to prevent the induction of radio frequency 7 current in the Fi circuit.

Considering, then, the operation of the embodiment shown in Fig. 2 it is to be understood that the ironcoresof chokes X1 an X; are partly magnetically saturated by the plate current from the source B. The interrupting frequency current in the separate windings decreases the flux density of, and hence increases the radio frequency inductance of the choke X1 simultaneously withthe increase of flux density, hence decrease of theradio frequency inductance of the choke X2 and vice versa." Thus, it will be seen that the direction of the efiective coupling of coil T to coil L is periodically reversed. Explained from the point of view of a balanced bridge operation; the functioning of the arrangement shown in Fig. 2 may be stated to be as follows:

X1 and X2 correspond to arms 22 and a; of

1. The two halves of coil T correspond to arms :21 and 23 of Fig. 1, while the total magnetic flux from coil T as a whole corresponds to the flux from coil T of Fig. 1. It would, of course, be possible to make Fig. 2 a complete bridge like Fig. l, but it is not necessary in order to get the desired results in Fig.

'In Fig. 3 there is-shown aseeond enibodiment of the basic principle shown in Fig. It. In

embodiment the device employed for periodically upsetting the balance of the bridge arrangement includingqthe coil T is quite different from the deviceutilized in Fig. 2. Here, again, the midpoint 5 of the coil Tof the bridge arrangement "is connected to the anodeofthe tube}, but through a direct current blocking condenser 8. The radio frequency choke T is connected between one terminal of the reproducer 3 and the junction of the anode of tube 2 and one side.

of the condenser 8. Each terminal of the feedbackco-il' T is connected to an arcuate metallic stationary plate 0. Thus, the arcuate plate 01 is connected to one side of the coil T, while the arcuate plate 02 is connected to the opposite side of the said coil. I

t will be noted that the plates 01 and c2 actually provide a metallic. ring which is split at diametrically disposed portions of the ring. At substantially the center of the ring there is disposedian axle or shaft A adapted to be driven plate V is. substantially equal to the width of the plates. (hand 02. It will be obvious, of course, that the rotor plate V in any angular position provides a certain amount of capacity with respect to the plate 0 and another amount of capacity with respect to the plate (:2.

The relative value of these capacities clearly depends upon the. angular position of the rotor TV. It will, thus, be seen that rotating the shaft A'atithe desired reversal frequency results in a periodic substitution of" reversed feed-back action by the coil T and coil L for the regenerative f eed back action between the same coils. This arrangement is equivalent in principle to a two throw single pole switch that alternately conheats the cathode to firstone end andthen the other end of coil T, thus periodically reversing the phase of feed-back to the grid circuit.

Fig. 3d is shownan arrangement that can he. used in place of the embodiment in Fig. 3. The fork leg A1 isdriven at the F1 frequency, thus varying, at the same frequency the position of the leg i/"l.

The relative values of the capacities c1-,.V1v and czvr will. depend upon the F1 frequency. Insteadoi a fork, a piezo-electric or magnetostriction' oscillator may be used, these devices being well known to those skilled in the art.

In Fig.4 there is shown another embodiment of the basic principle shownin Fig. 1. In the arrangement shown in Fig. 4 the feed-back coil T has one. of its terminal-s connected to a condenser the latter being shunted by a radio frequency choke coil lil. coil -T is again connected to the anode of tube The mid-point. 6 of the 2 through the blocking condenser 8. The other terminal of coil T is connected to the grid of tube 2-5; a grid biasing source C2 having its positive terminal connected to the cathode of tube 2 and" negative terminal connected to the common junction of the low potential terminals of the choke it and condenser 9. A radio frequency choke coil it is connected in series with the coil T and in parallel with the condenser 9 which is inshunt across the grid and cathode of tube 2'.

The anode of tube 2 is connected to the oathode oi tube 2" and to the positive side of source E1, the negative side. of said source being connected through the primary coil Ll of' transformer M, to the grid or tube 2". The anode of l3. to the cathode of tube 12, the sourceof interin dotted lines.

tube 2 is connected to the positive side of a potential source B2, and the negative side of said latter source is connected to thecathode of tube 2. A source of interrupting frequency voltage F1 is connected across the secondary coil H of the transformer The arrangement inlFig. 4 has for its purpose the obtaining of the same results as the arrange' ment shown in Fig. 3 without employing mechanic'al parts. The condenser 9 is balanced by the input capacity 5, shown-in do'tted'lines, oftubeil'. in the plate circuit of tube 2. The input capacity of tube 2 depends on the resistance of tube 2 which is varied above and below its normal value periodically by the interrupting frequency potential acting on the grid of the tube 2-. 'The chokes. i3 and 50 are employed to provide a-direot current path between the grid and cathode of tube 2, two chokes being utilized to preserve a balance between the impedances of the condensive branches, except as upset by the interrupting frequency, at all frequencies. Capacities 9' and C may be increased by the addition of actual condensers in parallel with them.

Another variation of the bridge arrangement in the anode circuit of tube 2 is shown in Fig. 5

wherein the armsof the bridge comprise three resistors 1'1, r2, rs, and the fourth arm of the bridge comprises a tube H2. "The anode of tube 12 is connected to the positive side of source B and to one terminal of the resistor T3. The feedbackcoil T is connected as the diagonal arm between points a and b, the coil T and the coil L being inductively coupled. The source of interrupting frequency current F1 is connected across the grid and cathode of tube l2. A condenser I3 is connected in shunt with the resistor T3. The operation of this arrangement may be described in the following manner:

When resistors T1, T2, T3 and condenser l3 are adjusted to balance the bridge for the radio frequency no-curr'ent flows in coil T. When alternating voltage is applied to the control electrode of tube [2, however, the plate circuit resistance or thistube is varied alternately above and below the balancing value, with the result that radio frequency current flows in coil T first in one phase and then in the opposite phase. There is produced in this way a periodic reversal of i the phase of feed-back from coil T to coil L.

Condenser I3 is added to compensate for the inherent plate to cathode capacity of tube 12.

Y "In each of Figs. 6 and 7, both of which show further variations of the bridge arrangement in i the anode circuit of the tube 2, the input circuit of' tube 2' in each of these figures is omitted for the sake of simplification. In Fig. 6 one terminal' of the feed-back coil T is connected in series with the anode of tube It through a resistor r. The latter is shunted by a condenser The other terminal of coil T is connected rupting frequency current F1 being connected between the cathode,v and'grid of tube 12. The inherent capacity between cathode and anode of tube: I 2 is denotedby the-numeral M and shown The bridge arrangement in 'Fig. 6 operates exactly the same in principle as that of Fig. 5', the only change being the substitution of a pair. of inductive arms fora pair of resistive arms, and the use of these inductive arms as.

the feed-back coil. A separate feed-back coil could, if desirable, be retained in which case it The tube 2" functions as a resistance would be Connected in parallel with the entire coil T.

In Fig. '7, the feed-back coil T is shown as the diagonaLarm of the bridge, the bridge arms in this arrangement comprising condensers l and I6, and a resistor i1 and tube I2. The resistor I1 is shunted by the condenser l3, and the cathode to anode capacity of tube [2 is denoted'by the reference numeral IB shown in dotted lines. Here, again, the source of'interrupting frequency current F1 is connected between the cathode and grid of tube 2. The operation of this arrangement is the same as that of Fig. 6, the only change being that a pair of capacitive arms are substituted for a pair of resistive arms and condenser I3 is located across the single'remaining resistor- It should be clear from the above description of Figs. 2 to '7 inclusive that the electrical structure of the bridge 4 of Fig. 1 may assume widely different characteristics. The impedance 2 of the bridge 4 has been shown to be in each of Figs. 2 to 7 inclusive, resistors, inductances or capacities. Hence, it should be clearly understood that while I have shown and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims,

For example, the bridge method here-disclosed for reversal of phase of feed-back may also be practiced on the input side of the superregenerative circuit. That is, a simple tickler coil in the plate circuit may be coupled to the input resonant circuit in a fixed manner, while the input resonant circuit and the tube input electrodes form conjugate arms of a bridge whose balance is periodically upset in first one direction and then the other at a desired rate by means such as already described in connection with Figs. 2 to 7. Furthermore, it is obvious that the feed-back 'means need not be the single tickler or mutual inductance feed-back so far discussed. Broadly speaking any feed-back circuit the phase of whose feed-back maybe periodically reversed by unbalancing means, may equally well be employed.

What I claim is:

1. A super-regenerative circuit comprising an electron discharge tube having an output circuit and a resonant input circuit, a normally balanced electrical system having a pair of conjugate neutral points disposed in said output circuit, said system including. an inductively reactive element connected across said neutral points electrically coupled to said input circuit, and means electrically connected with said system for periodically unbalancing the system to reverse the phase of feed-back between said element and said input circuit.

so that said neutral points are at substantially the same potential, and periodically disturbing said condition first in one direction and then in the other to provide a periodic reversal of the phase of potential between said neutral points andof feed-back between said output and input circuits.

A. The method of amplifying varying electric currents in an amplifier provided with input and output circuits which comprises impressing the varying potential of the current to be amplified upon the input circuit, establishing an electrically balanced condition in the output circuit, electrically coupling the output circuit to said input circuit so that there is no feedback in said balanced condition, and periodically disturbing said condition at a super-audible frequency whereby the phase of feed-back between the output and input circuits will be periodically reversed.

5. In apparatus for amplifying varying electric currents, an electron discharge tube provided with an output circuit and an oscillatoryinput circuit, a normally balanced bridge having a pair of conjugate neutral points in said output circuit, and means electrically connected to said bridge for periodically varying the total efiective resistance of said input circuit about a mean value greater than zero, said bridge including an inductively reactive element connected across said neutral 7 points and electrically coupled to said input circuit.

6. A receiving circuit comprising a tube having an output circuit and a resonant input circuit, a normally balanced bridge in said output circuit, and a source of super-audible interrupting frequency current coupled to said bridge in such a manner that the bridge is periodically unbalanced first in one direction and then in the other and a feedback connection between a portion only of said bridge and said resonant input circuit.

'7. In an electrical circuit, a space discharge device provided with an input circuit and an output circuit, a bridge in said output circuit for normally establishing an electrically balanced condition therein, means including an inductively reactive element connected to opposite neutral points of said bridge and arranged to transfer energy from said output circuit to said input circuit, and additional means operatively connected with said bridge for periodically disturbing said normally balanced condition whereby the phase of said transfer is periodically reversed.

8. In an electrical transmission network, an

electron discharge tube provided with an oscillatory input circuit and an output circuit, a normally balanced bridge connected in said output circuit including at least four impedances, one of said impedances being coupled to said input circuit to provide an energy transfer path to the latter, and means electrically connected with at least one of the impedances'of said bridge for periodically unbalancing the bridge in such a manner that the phase of energy transfer between the output and input circuit of the tube is periodically reversed. I

9. In a repeating circuit, an electron discharge tube provided with a resonant input circuit and an output circuit including a normally balanced bridge comprising at least two impedances and a coil inductively coupled to said input circuit, and a source of interrupting frequency current electrically connected with at least one of the impedances of said bridge, other than said coil. for

periodically unbalancing the bridge whereby the phase of feed-back between said coil and said input circuit is periodically reversed.

10. In an amplifier circuit, an electron dis-- charge tube provided with an oscillatory circuit across its input electrodes, said input circuit being tuned to a desired radio frequency, a normally balanced bridge network having a pair of conjugate neutral points connected between the anode and cathode of the tube, said network including an impedance connected across said neutral points and coupled to said input circuit for the transfer of radio frequency energy thereto, and means for disturbing the balance of said bridge in such a manner as to periodically reverse the phase of energy transfer between said impedance and said input circuit.

11. In combination, a single electron tube, having a grid and a plate circuit, opposing and substantially equally effective means serially connected in said plate circuit for feeding back energy from the plate circuit of said tube to its grid circuit, and further means for upsetting at a super-audible frequency the balance between said opposing feed-back means whereby the net feed-back is periodically reversed in phase.

12. A vacuum tube having a grid and a plate circuit, a balanced bridge network serially connected in said plate circuit and having a pair of conjugate neutral points, an inductively reactive impedance element connected across said neutral points and electrically connected to said grid circuit and means for rapidly varying the value of an element of said bridge network above and below its normal value whereby the bridge is unbalanced and an alternating current of high frequency flows through said impedance element.

13. A super-regenerative amplifier comprising a thermionic tube having an output circuit and an input circuit, a normally balanced bridge circuit having a pair of conjugate neutral points disposed in said output circuit, a circuit connected across said neutral points comprising an inductively reactive element coupled to said input circuit, a mechanical element electrically connected to said bridge circuit and means for operating said mechanical element at a high speed to periodically unbalance the bridge cirtube, said bridge network including a coil inductively coupled tosaid input circuit and two condensers having a common electrode and mechanical means connected to said common electrode for rapidly moving it adjacent the other condenser electrodes to unbalance said bridge net- Work.

WALTER VAN B. ROBERTS. 

